This invention relates to a light barrier optical module comprising at least one optical emission or reception element with an optoelectronic emission or reception component, together with an optical transmission device to exchange a light beam with a corresponding element in another light barrier module, to form a light barrier between them composed of at least one light beam.
There are various existing types of light barriers formed of distinct emission and reception elements assembled on each side of an area to be monitored so as to form light beams between the two modules, such that the receiving optoelectronic component emits a break signal when an obstacle (person or object) interrupts the beams. This signal then controls an action, for example switches off a machine.
These light barriers comprise optical modules each formed of several optical emission and reception elements; each emitting element cooperates with a corresponding receiving element in the other module to define a narrow light beam forming part of the optical barrier; an interruption to one or several light beams is detected and the resulting signal is used as described above.
Depending on the case, a barrier is composed of two optical modules placed at each end of the barrier. One of the modules is composed of emitters and the other is composed of receivers. It would also be possible to distribute emitters and receivers between the two modules. Finally, the barrier may be composed of a module with associated emitters and receivers, the light beams being reflected at the other end of the barrier.
Usually, optical modules include a lens associated with each optoelectronic component to give priority to part of the space, and consequently concentrate energy. This lens increases the effective area of the component and unfortunately this coupling between the emission module and the reception module or between the component and the lens introduces risks of multiple reflections widening the emitted or incident radiation in the vicinity of the lens, to exceed values predicted by geometric optical theory and correspondingly the optoelectronic emission or reception component.
Rays emitted within the optical cone that do not reach the corresponding reception lens are in principle lost rays. In practice, the situation is different because there may be multiple reflections on structures surrounding the light barrier and these multiple reflections result in incident rays reaching the optoelectronic reception component through the reception module lens, despite the relatively high angle of incidence.
It has already been proposed to attenuate the reflecting capacity (albedo) of the element in the module located at the reception. This is done by applying a non-reflecting coating on the inside surface of the orifice of the component, and forming striations or small steps to prevent multiple reflections from reaching the reception optoelectronic component. Unfortunately, these solutions are not satisfactory, either because they are not effective or because of difficulties in manufacturing them industrially.
To overcome these disadvantages, the regulations imposed specific conditions about emission and reception. Thus, the emission beam must have an aperture angle of not more than 2xc2x0 for a distance of 3 meters, for a maximum security light barrier category. These conditions are not easily satisfied with existing solutions.
The purpose of this invention is to correct these disadvantages and to propose a light barrier optical module that prevents multiple reflections of emitted light beams that could get around the obstacle passing through the light barrier and which has to be detected, and by simplifying manufacture of the device, rather than further complicating it.
Consequently, the invention relates to an optical module for a light barrier of the type defined above, characterized in that the emission and/or reception element comprises a wall associated with entry of the beam into the component or its exit from the component, and provided with an orifice and in that it comprises at least one partition forming a diaphragm between the component and the optical transmission device.
Due to the orifice in the partition which forms a diaphragm between the beam entry or exit orifice in the component and the optical transmission device, both in the emission direction and in the reception direction, the optical module according to the invention is capable of eliminating parasite beams originating from reflections on parasite surfaces not located on the light beam between the light barrier emitter element and receiver element. Very schematically, the partition orifice corresponds to an orifice surrounding the cone or truncated cone joining the useful area of the optical transmission device, for example a lens, to the useful area of the component both in the interval between the partition and the lens, and between the partition and the component, in order to trap light rays at large angles of incidence, and provide the optical module with a high degree of detection reliability using simple means.
According to another characteristic of the invention, each element comprises at least two thin partitions separated from each other and from the optical transmission device and the optoelectronic component, to form at least three intervals in which parasite light rays are trapped.
Preferably, the module according to the invention comprises a body formed of a front wall and a back wall separated by at last one thin partition in which an orifice is formed, the walls and partitions being connected through spacers, the front wall being provided with a front orifice aligned on the optical center line of each element, the back wall being provided with an orifice through which the beam enters into or exits from the optoelectronic component on the center line of the element, a front panel with lenses which is fixed on the front wall, each lens being located on the center line of the element.
In particular, the module may be made by injection molding using a mold with mobile parts between which the front wall, the back wall and the partitions are defined, and these mobile parts are positioned or extracted in the direction transverse to the injection mold. The orifices in the front wall and in the intermediate partitions, and possibly in the back wall, are made using a broach. It is not difficult to extract the molded product since the shape of this broach is necessarily conical (possibly but not necessarily truncated) with the large base located at the outside. The taper on this broach is beneficially the same as the taper to be applied to the detection beam, taking account of the parameters of the optical system (lenses) of this element.
Beneficially, the module comprises attachment means in a housing.
Finally, the body comprises positioning broaches that project from its front surface and the front element equipped with lenses is provided with recesses in positions corresponding to the broaches in order to position this front element on the broach.
According to another advantageous characteristic, the module comprises 16 elements and the front wall is formed of two parts, each part being equipped with eight lenses.